Semiconductor devices are being developed to including an increasing number of components which also increases the required number of input/output leads. This increase in input/output leads has required the development of finer pitch lead tips on the lead frame.
The prior art process of making lead frames by etching utilizes a solid metal strip that is laminated on both sides with a photoresist material. Both sides of the photoresist material is exposed to a light though a pattern that defines the lead frame configuration. The photoresist is then developed to remove photoresist in areas that are to be etched to remove the unwanted metal from the metal strip.
The laminated metal strip with the patterned photoresist is then etched to define the metal lead frame. After the etch process, the leads of the lead frame are defined and are separate from one another. The etched leads are subject to damage during the remaining lead frame formation process.
After etching, the photoresist is striped or removed from the lead frame. The lead frame is then plated. Wire bond contact areas may be electroplated.
After plating, the leads of the lead frame are taped to hold them in their respective positions. The lead frames, which generally are formed in continuous strips, are then cut to length, having one or more lead frames on a stip.
The problems that exist with fine pitch leads on the lead frame has been addressed in U.S. Pat. No. 5,454,905, where the leads of the lead frame have two different thicknesses. The outer portion of the lead frame lead has a thickness greater than the inner portion adjacent to the semiconductor die. The inner portions of the lead frame leads have been etched to a less thickness than the outer portions of the lead frame leads.